The most common and most likely answer to this crossword clue is the 5 letter word CELLO
C
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L
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O
More clues leading to the result CELLO
- In small room, old musical instrument
- Musical instrument in simple room, old
- Instrument in small room close to piano
- Instrument in place of confinement, centre for prisoners
- Instrument in Purcell overture
- Instrument, old, at rear of brother's room
- Little room with old instrument
- Little room, inside case, for musical instrument
- Transparent sheet left over instrument
- Little chamber orchestra's first instrument
Buddy explains!

The straight part
We know that "Instrument" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case instrument = cello.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CELLO mean?
CELLO noun- A large stringed instrument of the violin family with four strings, tuned from lowest to highest C-G-D-A, and played with a bow, also possessing an endpin to support the instrument's weight.
- Cellophane